5 Most Amazing Caves

Naica Mountain

Naica, Mexico

In Naica, Mexico, volcanic activity created conditions that would one day lead to an amazing discovery: A cave housing what may be the largest crystals in the world.

Cueva de los Cristales, or the Cave of Crystals, is a natural marvel of cause and effect. A volcanic eruption built Naica Mountain, depositing tons of anhydrite, which is a high-temperature form of gypsum. When the magma beneath the mountain cooled, the anhydrite dissolved into molecules that seeped down with the water. Beneath the mountain, those molecules came out of solution and crystallized, creating gypsum crystals that have grown to lengths of up to 36 feet (11 meters) [source: Lovgren].

These crystals are most likely unmatched anywhere in the world, due to the unique conditions of the Naica caves in terms of both water flow and temperature range. Some have compared the sight to Superman's home -- mammoth, glittering crystals jutting out from every surface. But only a relative few have seen the Cave of Crystals up close. Discovered in 2000 by a couple of miners, Cueva de los Cristales is part of an active mine, and it gets so hot down there that the cave researchers and journalists who have gotten a peek have had to wear full protective gear.